More disk space for fs.apt.emulab.net

We only have 2TB in the ZFS pool on fs (aka ops). Ideally, we would have more like 12TB as we do on Emulab, Wisconsin and Clemson. However, the control node on Apt only has 5TB in total. I need to see if there is space to add additional drives to expand the storage. Or we could replace the existing drives with larger ones, which would involve copying all data off and back on again.